The present invention relates to a procedure for taking a reference measurement, respectively for recalibrating an optical measuring device used in determining surface quality.
Devices employed to determine the quality of surfaces of a wide variety of products are known in the prior art. Since surface quality is a crucial characteristic for many products in providing the total overall impression of the product, the quality of these products"" surfaces often takes on special significance. For this reason, measuring devices are employed in order to qualitatively and quantitatively determine the visual properties of a surface.
Such measuring devices are exposed to dust and other contaminations in particular, but not limited thereto, in the production environment, causing the optics of such a device to become dirtied over the course of time, which in turn changes its transmission properties and may yield erroneous measurements. Therefore, conventional devices undergo routine maintenance at regular intervals.
Another problem arising in surface determinations is that individual elements in the devices age. Especially when using thermal light sources which include filaments, a portion of the filament will vaporize over time, settling on the inside of the surrounding glass bulb and changing the transmission characteristics of the glass bulb such that the light emitted from the light source will exhibit an age-induced spectral change.
The relative position of the light-radiating elements and the sensors to one another can also vary due to the effects of vibrations or jarring impacts, etc., so that the geometrical relational ratios within a measuring device can vary over the course of time.
Consequently, in order to obtain high quality measurements, many of the measuring devices known in the prior art are calibrated, respectively recalibrated, on a frequent basis. In so doing, the measuring device is placed on a surface having known properties and these properties are then determined with said measuring apparatus. The user can then balance or calibrate the device to zero, respectively to a particular deflection, for example by changing potentiometer resistance, so that any deviations in the devices can be compensated for to a certain extent.
To simplify operational handling, automatic calibration procedures are also known in the prior art which automatically recalibrate the measuring device to the corresponding reference value after a reference surface has been measured.
A disadvantage of the known prior art procedures and devices, however, is that many operator errors are not detected. A user frequently relies on the automatic mechanisms of such devices instead of, for example, scrutinizing the optical devices himself and controlling whether said devices are dirtied.
It is therefore the task of the present invention to provide a procedure as indicated above in order to enable making a reliable and reproducible reference measurement for calibrating or recalibrating an optical measuring device.
This task is solved in accordance with the present inventive procedure as defined in claim 1.
Further preferred embodiments of the invention constitute the subject matter of the subclaims.
A procedure according to the present invention for making a reference measurement is performed using an optical device which has at least a first illuminating means comprising at least one source of radiation and which is aligned at a predetermined angle to the measurement surface.
The optical device furthermore comprises at least a first and at least a second optical measuring means, both also aligned at a predetermined angle to the measurement surface and both receiving a portion of the light reflected from said measurement surface.
Both the first as well as the second optical measuring means in each case comprise at least one photo sensor which emits an electrical measurement signal which is in each case characteristic of the received, respectively reflected, light.
A control and evaluation means having at least one processor means and at least one memory means is additionally provided in the optical device in order to control the measurement sequence and to evaluate the measurement results. An output means is provided in the optical device for the outputting of the values.
The procedure according to the present invention using the optical device comprises the following steps which may be performed in the following or in a different order:
a) in a first step, the optical device and the reference surface are aligned with respect to one another; preferably, the optical device is placed upon the reference surface.
b) the first optical measuring means subsequently takes a measurement which is then preferably stored in the memory means.
c) a deviation parameter is derived from the measured value taken by the first measuring means and a first calibration value stored in the memory means which is characteristic of the first optical measuring means, said deviation parameter is a measure of the measured value""s deviation from said first calibration parameter.
d) the next step entails the taking of a measurement with the second optical means.
e) after taking the measurement with the second measuring means, a second deviation parameter is derived from the measured value from said second measuring means and a second calibration parameter stored in the memory means which is characteristic of the second measuring means.
f) a variance parameter is derived from the first and the second deviation parameter, and
g) a subsequent warning signal is issued when the variance parameter either exceeds or falls short of a certain range, or when the variance parameter is greater than a predetermined value.
The procedure according to the present invention has numerous advantages.
Upon employing the optical device for the first time, which usually takes place while still in the production or quality control stage, the device is first adjusted by means of measuring reference standards and making the corresponding precision fine-tuning.
High-quality measuring devices need to be recalibrated at regular intervals in order to essentially equalize, respectively exclude, any changes in geometric circumstances. Therefore, reference surfaces are provided for many measuring devices which have specifically known and defined properties; these reference surfaces may also correspond to the reference standards of the original precision adjustment.
In conventional measuring devices, at least within the scope of the final inspection or the precision adjusting stage, the measuring device is preferably placed upon at least one reference surface and the device then measures said reference surface. The relevant measured value is then stored as the calibration parameter in a memory of the measuring device, respectively printed in the product specification. When such a measuring device needs to be recalibrated during the course of daily operation, it is then placed upon the relevant reference surface and measures the properties of said reference surface.
By comparing the values as thus determined with the calibration parameters stored in the memory means, respectively the printed calibration parameters, the device can be accordingly re-adjusted, thus allowing for a nullifying, at least to a certain extent, of effects as induced by contamination and other such similar factors.
However, it is frequently the case with measuring devices and procedures as known in the prior art for taking, respectively analyzing such a calibration or reference measurement, that these reference measurements are carried out incorrectly.
The procedure according to the present invention has the advantage with respect to the known methods that the measurement results of the first and of the second measuring means are subjected to a plausibility check, allowing for the avoiding of many erroneous reference, respectively calibration, measurements. It is not solely the problem that incorrect reference measurements need to be repeated in order to achieve high-quality meaningful measurement results, it is also the problem that many of these types of errors in reference or calibration measurements are only detected at a later point in time, meaning that, among other things, a number of measurements using the incorrect reference measurements may already been made in the ongoing production operations. Should such errors not be discovered until hours, days or even weeks later, a great number of flawed products may meanwhile have been manufactured during that time frame and to manufacture them anew translates into high expenditure. Neither can the damage to a company""s image arising in the context of distributing flawed products be disregarded.
It is often the case with such types of measuring devices that one of its optics is defiled by, for example, a fingerprint while the other optic is essentially still unblemished. Such circumstances can be reliably determined with the procedure according to the present invention. First a measurement is taken by each optical measuring means during the course of the reference or calibration measurement and a deviation parameter is determined for each respective optics by means of a comparison with each respective calibration parameter stored in the memory means. In the cited example in which one of the optics is contaminated by, for example, a fingerprint, this means that the deviation parameter for this optic will be of a relatively high value while the deviation parameter for the unsullied optic will be small. A variance parameter, derived from the first and the second deviation parameter, will in this case therefore exhibit a relatively high value.
Thus, the procedure according to the present invention enables the quick and reliable determining of faulty reference measurements which may be due to, for example, partially soiled optics so that a warning signal can be emitted and the reference measurement can be re-taken, if necessary, following cleaning of the optics.
In a preferred embodiment of the procedure according to the present invention, at least one of the deviation parameters of the first or the second optical measuring means is derived from the difference between the measured value of the respective measuring means and the respective calibration value, whereby the first deviation parameter and the second deviation parameter in this case is preferably equal to the difference between the respective measured value and the first, respectively second, calibration parameter.
The forming of a deviation parameter from the difference between the measured value and the calibration value is advantageous since small deviations lead to small deviation parameters, while large deviations lead to accordingly larger deviation parameters.
In another preferred embodiment of the present inventive procedure, at least one deviation parameter, i.e., either the first deviation parameter or the second deviation parameter, is derived from a ratio between the corresponding measured value and the corresponding calibration value.
In a further preferred embodiment of one or several of the previously described embodiments, a warning signal is preferably emitted by said output means when the first and/or the second deviation parameter departs from a certain given range; i.e. exceeds or falls below a predetermined value.
This embodiment of the present inventive procedure is highly advantageous since other different possible errors can be reliably determined upon taking a reference or calibration measurement.
In this respect it may be possible, for example, that the illuminating means is dirty or that the radiation source in the illuminating means is defective, so that the radiation source is not emitting at any intensity or only very low intensity. Should a reference value in this case be taken with the first measuring means and the second measuring means, the measured signal will be very low; as a consequence, the error rate from this measurement sequence will be especially high. The deviation parameters derived from the measured values and the corresponding calibration parameters in this case are relatively large such that while both measuring means have, for example, a similar deviation and possibly only a small variance parameter has been determined, the error can be reliably detected in the reference measurement.
It is likewise possible, by means of limiting the deviation parameters, to reliably determine a flawed or contaminated reference surface. Should a reference surface be contaminated, this leads to lower measured values and without the procedure according to the present invention, would lead to an incorrect reference value and thus all subsequent measurements would likewise be faulty.
By the emitting of a warning signal upon one of the deviation parameters either exceeding or falling below an allowable range, contaminated reference measurement surfaces can be reliably detected.
It may furthermore be the case that a user employs an incorrect or unsuitable reference surface for calibration when making a reference measurement. These types of errors may also be essentially reliably avoided by means of limiting of a deviation parameter.
In a further preferred embodiment of the procedure according to the present invention, a warning signal is emitted when at least one of the measured values, taken with the first or the second measuring means while making the reference measurement, exceeds or falls short of a predetermined range.
This offers the advantage that the absolute measure of the individual measured values can be taken into consideration when assessing a reference measurement.
In all of the described embodiments, the first and/or the second deviation parameter can be derived from the original calibration parameter (from the initial precision adjustment) and the corresponding measured value.
It is also possible to derive the deviation parameter from the most recently saved calibration parameter (e.g. the measured value of the most recent valid reference measurement) and the current measured value.
In this variation, a measured value gradient is formed from that between the most recent reference measurement and the current measurement. A warning signal issues upon this gradient exceeding a predetermined and/or a selectable magnitude.
In a preferred embodiment of the present invention, the variance parameter is derived from the difference between the first and the second deviation parameter; in accordance with another embodiment, the variance parameter is derived from a ratio between the first and the second deviation parameter.
In another preferred embodiment of the present invention, the variance parameter is determined using a mathematic operation such as, for example, a linear, logarithmic or exponential calculation or other such similar calculations. Using a suitable mathematic operation allows for making even enhanced considerations of deviation parameters or measured values which, for example, exceed or fall short of a certain measure so that even further fine-tuned relevant assessments can be made with regard to the type of measurement (gloss, color, etc.).
In one or all of the previously described embodiments of the present invention, the optical device comprises a second illuminating means having at least one light source, its light directed at a predetermined angle to the measurement surface. According to the present preferred embodiment, it is especially preferred that the first illuminating means is arranged symmetrically to the first measuring means and especially preferred is that the second illuminating means is arranged symmetrically to the second measuring means.
It may however also be the case that the individual illuminating and measuring means are aligned at differing angles to the surface, whereby the predetermined angles at which the individual means (illuminating and measuring means) are aligned to the perpendicular of the surface to be measured can be angles of 0xc2x0, 5xc2x0, 10xc2x0, 15xc2x0, 20xc2x0, 30xc2x0, 40xc2x0, 45xc2x0, 50xc2x0, 60xc2x0, 70xc2x0, 75xc2x0, 80xc2x0, and 85xc2x0 or other such similar angles. The arrangement of the angles when employing the inventive procedure also depends upon the measurement task the optical device is to perform.
In accordance with a preferred embodiment of the present invention, at least one of said deviation parameters, variance parameters and preferably measured reference values is stored essentially permanently in the memory means upon every reference measurement, whereby especially preferred is the essentially permanent storing in the memory means of at least the first and the second deviation and variance parameters.
This has numerous advantages in that the storing of the individual values also enables the taking of previous reference measurements into account when assessing the currently measured values, respectively deviation parameters, respectively variance parameters.
In accordance with a further preferred embodiment, a table means is provided in the memory means into which at least one of said parameters and preferably the first and the second deviation and variance parameters are essentially permanently stored on a line or similar object of said table for essentially each reference measurement. A measurement time parameter is preferably additionally stored upon each measurement. Thus the parameters from preceding reference measurements are essentially permanently available, and a warning signal can issue upon two consecutive reference measurements exhibiting a deviation, meaning for example a ratio or a difference between two consecutive parameters or measured values, which exceeds a predetermined magnitude.
As an example, a warning signal can be emitted when the deviation parameter from the nth reference measurement of one of the optics deviates by a certain amount from the deviation parameter from the (nxe2x88x921)th reference measurement of the corresponding optics. Such a configuration also enables the inventive procedure to be applied with an optical device having only one optical measuring means. The previous reference measurements then serve as the reference measurement control and a warning signal is emitted when the measured value recorded from a reference measurement differs from the next reference measurement by an amount which is greater than a predetermined value. The applicants point out that they reserve the right to also claim protection for such a procedure.
In a further preferred embodiment of one or several of the previously described embodiments and configurations of the present invention when assessing a reference measurement, the table means provided in the memory means may be evaluated using statistical selective processes as are known in the prior art.
Should, for example, an offset line yield through linear regression of respectively each of the reference values of the first measuring means and the measured values of the second measuring means (when applicable), a reference measurement can be rejected, respectively a warning signal can be emitted when the current measured value deviates from said offset line by a predetermined measure.
This configuration enables that, for example, a slight increase in contamination can be tolerated as long as contamination does not reach too high of a measure. It simultaneously allows for reliably detecting errors in a reference measurement.
In all of the previously described configurations and embodiments, the warning signal is preferably emitted by the output means, whereby this task can ensue visually, acoustically or in another manner. It is also possible that the warning signal is emitted to a central device via radio or other similar means.
It is also possible that the inventive procedure is carried out using a device which has a plurality of three, four or more measuring means. Deviation parameters can then be determined for all or two, three or more of said measuring means.
Should a warning signal be emitted, the inventive procedure can decline acceptance of the measured value so that the user is required to, for example, re-confirm the value or first be required to eliminate the source of the error before a valid reference or calibration measurement will be accepted.